1. Field of the Invention
This invention relates to the selective conversion of hydrocarbons. More particularly, this invention relates to the selective hydroconversion of waxy, normal paraffin type hydrocarbons present in hydrocarbon oil feedstocks to lower boiling hydrocarbons. Still more particularly, this invention relates to a process wherein waxy hydrocarbons present in petroleum feedstocks are selectively hydrocracked to hydrocarbons boiling below the boiling range of the feedstock and wherein the aromatics content of said feedstock is simultaneously reduced by contacting the feedstock and hydrogen with a catalyst comprising at least one catalytic metal component and a hydrogen from Zeolite L crystalline alumino-silicate and recovering a product having a reduced wax content.
2. Description of the Prior Art
It is well known in the art to dewax wax-containing mineral oils, particularly the lube oil fractions of petroleum oil, in order to remove at least a portion of the wax therefrom to obtain a dewaxed oil of reduced pour point. For many years this wax has been removed via various solvent dewaxing processes. In solvent dewaxing processes the temperature of the wax-containing oil is lowered sufficiently to precipitate the wax therefrom as solid crystals of wax. At the same time, solvents are added to the waxy oil in order to improve the fluidity and reduce the viscosity thereof so that various filtration or centrifugation processes can be used in order to separate the wax from the dewaxed oil. Wax anti-solvents such as ketones are often added to decrease wax solubility in the oil-solvent mixture. There is usually a pour-filter temperature spread in solvent dewaxing processes. That is, the wax filtration temperature must generally be around 10.degree. to 20.degree. F. lower than the pour point requirements of the dewaxed oil.
Concomitant with the world-wide decreasing supply of naphthenic crudes heretofore used to make very low pour point oils such as transformer oils, there has been an increase in the demand for these oils due to the continuously increasing demand for electrical power. Transformer oils used in colder climates generally have a pour point requirement of around -50.degree. F. It is technologically unfeasible to obtain these low pour transformer oils via solvent dewaxing of paraffinic oils, because of the extremely severe refrigeration requirements. White oils are highly refined petroleum oils which must meet various requirements including haze-free water whiteness and are generally produced from naphthenic stocks which sometimes contain around 1 or 2% wax. This was can affect the pour point of the oil and results in a haze which is cosmetically objectionable. It is also technologically unsound to solvent dewax these white oils. Certain middle distillate fuels must also have low pour points so that the fuels do not congeal at low temperatures. This is especially true for jet fuels.
In recent years, various catalytic dewaxing processes have been proposed, although none of these processes has yet been commercially adopted by the petroleum industry. For example, U.S. Pat. No. 3,039,953 discloses a catalytic process for dewaxing wax-containing hydrocarbon oils wherein the normal paraffinic wax constituents contained therein are broken into lower molecular weight olefins and gases using crystalline alumino-silicate Zeolites such as chabazite, analcite and mordenite having a uniform pour opening of about 5 .ANG.; U.S. Pat. No. 3,395,096 discloses a process for selectively hydrocracking straight chain hydrocarbons contained in hydrocarbon feedstocks, which is useful for dehazing white oils and dewaxing lube oils, using a rare earth promoted Zeolite A or erionite having uniform pour openings of less than about 6 .ANG.; U.S. Pat. No. 3,625,880 claims selectively removing normal paraffins from hydrocarbon feeds using erionite that has been at least partially decationized. Molecular sieves such as erionite have been found to be useful for catalytically dewaxing and dehazing lighter fuel fractions ranging up to and through fractions such as jet fuel. However, when higher boiling fractions such as lube oil fractions are catalytically dewaxed using catalysts such as erionite, coke very quickly builds up on the catalysts thereby deactivating them.
More recently, it has been found that mordenite, particularly the hydrogen form of mordenite commonly referred to in the art as decationized or H-mordenite, and certain ZSM-type crystalline alumino-silicates are effective in catalytically dewaxing the heavier petroleum oil fractions such as lube oil fractions. U.S. Pat. No. 3,516,925 and U.S. Pat. No. 3,539,498 disclose catalytically dewaxing these heavier hydrocarbon oil fractions over a decationized or hydrogen form of mordenite. The mordenite preferably contains a hydrogenation component selected from one or more Group VI and VIII metals and oxides thereof. The wax-like hydrocarbons, particularly the normal paraffin types, are selectively hydrocracked into lower boiling hydrocarbons which are primarily gases at room temperature, thereby producing a dewaxed oil product having a substantially lower wax content and pour point, but whose boiling range is the same as the boiling range of the feed. U.S. Pat. No. 3,700,585 discloses the use of crystalline alumino-silicates of the ZSM-5 and ZSM-8 type for catalytically dewaxing both normal and slightly branched paraffins from hydrocarbon fractions such as jet fuel and lube oil fractions.
A number of improvements and additions to the use of decationized or hydrogen form of mordenite and/or ZSM-5 crystalline alumino-silicates have been made. U.S. Pat. No. 3,663,430 discloses that superior results are obtained if the mordenite catalyst contains a silica-to-alumina ratio of at least 20:1, while British Patent No. 1,134,014 discloses that the silica/alumina ratio of the mordenite should be at least 14:1. U.S. Pat. No. 3,438,887 discloses a three-step process for producing lube oils comprising solvent refining followed by catalytically dewaxing over hydrogen or decationized mordenite and then hydrorefining the solvent refined, dewaxed oil. U.S. Pat. No. 3,647,681 discloses an improvement to catalytic dewaxing processes employing decationized mordenite as a catalyst wherein the improvement comprises poisoning or blocking off the surface sites of the catalyst by laying carbon down thereon so that the catalyst contains at least 1/2 wt. % of carbon before it is used for catalytic dewaxing. Higher yields of dewaxed product are claimed by the use of this invention. U.S. Pat. No. 3,986,982 discloses an improved method for regenerating H-mordenite which has been deactivated during a catalytic dewaxing process and suggests that this regenerating method may also be applicable to other Zeolites such as Zeolite Y, T, L, erionite and offretite. Similarly, U.S. Pat. No. 3,894,938 and U.S. Pat. No. 3,956,102 disclose improvements in the use of ZSM-5 type zeolites in catalytic and hydroprocessing processes.
The prior art teaches that various other types of crystalline alumino-silicates are not suitable for use in catalytic dewaxing processes. U.S. Pat. No. 3,539,498 mentions that faujasite and types A, X, Y and L synthetic zeolites are capable of selectively adsorbing particular hydrocarbon types from each other, but does not suggest that any of these materials could be used in a catalytic dewaxing process. Further, U.S. Pat. No. 3,956,102 teaches that large pore size crystalline alumino-silicates or zeolitic molecular sieves represented by zeolites of type X, Y and L, admit all components normally found in petroleum distillate charges and are therefore unsuitable for use in catalytic dewaxing or hydrodewaxing processes and that only those which have a pore size of approximately 5 .ANG. and the ZSM-5 type are suitable because they will admit only normal and/or slightly branched paraffins present in a hydrocarbon feed charge. This prior art contention is re-enforced in U.S. Pat. No. 3,968,024 directed towards an improved catalytic hydrodewaxing process employing ZSM-5 type zeolites, wherein the same crystalline alumino-silicates (X, Y and L) are mentioned for one purpose or another, but are not suggested as being useful for catalytic dewaxing processes. Similarly, U.S. Pat. No. 3,663,430 discloses that Zeolites A, X and Y were tried and found to be unsuitable. Therefore, in view of the teachings of the prior art, the instant invention was surprisingly unexpected.